Dynamic Alignment of Artificial Legs with the Adjustable Coupling

ANTHONY STAROS, M.S.M.E.1

SINCE World War II one of the most signifi what different type of function, is a question cant advances in limb prosthetics has been able procedure; i.e., alignment suitable for a the introduction of rational principles for constant friction unit may not make proper fitting and aligning artificial legs (2,11). The use of the functions provided by more sophisti University of California (Berkeley—San Fran cated devices. Some prosthetists have learned cisco), sponsored by the Veterans Administra to accommodate for the required deviations by tion, has been primarily responsible for the rules of thumb, but essential are some method steady improvement in methods and devices and some tool for dynamic alignment to be used by prosthetists in artificial-leg construc made directly on the knee or knee-shank-foot tion. mechanism to be used in the final prosthesis. To assist the prosthetist in carrying out these Ideally, the device should be of simple design principles, a number of mechanical aids or tools and useful for both above-knee and below-knee were devised. The two adjustable legs—one cases. For the above-knee case, such a device for above-knee cases (Fig. 1), the other for should be inserted between the socket and cases below the knee (Fig. 2)—and an align permanent prosthetic knee for "functional" ment duplication jig (Fig. 3) were developed alignment. by the University of California, and are now If the unit were simple enough, it would recognized as important tools of the prosthetist be expected that more generalized use of (4). And dynamic alignment of artificial legs is alignment tools might result, and that facilities a standard part of the curriculum of prosthetics in other countries, where it is difficult to schools (1) and standard operating procedure procure adjustable legs, could enjoy the ad in most limbshops. vantages of dynamic alignment. Moreover, But there have been problems. For one, the the alignment-transfer process needed scrutiny limbshop must have a minimum of two ad to see if simplifications in the equipment justable legs for adult cases, and two smaller necessary might result. ones for child cases. A shop of any size requires For these reasons, the VA Prosthetics multiple quantities because frequently a given Center developed the Adjustable Coupling, unit must remain attached to a socket for a sometimes termed the "Staros-Gardner Cou particular amputee for an extended period of pling." time. And to make best use of the adjustable legs an alignment transfer jig is needed. DESCRIPTION OF THE ADJUSTABLE COUPLING Other limitations in the above-knee adjust able leg appeared when knee units or knee- The adjustable coupling (Fig. 4) consists shank-foot units with fairly complex functions essentially of two plate assemblies held to were introduced. Use of the UC adjustable gether by a central toggle pin. Mounted to a AK leg, with its single-axis, constant friction middle or intermediate plate but part of one joint for achieving alignment which is to be plate assembly are four screw subassemblies, transferred to a permanent leg having a some- spaced 90 deg. apart, which contain indepen 1 Chief, Veterans Administration Prosthetics Center, dently adjustable, knurled screws used to 252 Seventh Ave., New York 1, N. Y. "lock" the entire coupling as well as to provide

31 32

Fig 2. A below-knee adjustable leg used in current practice.

and intermediate plates both contain "A" and "P" marks to indicate the anterior and pos terior sides, respectively. The two assemblies contain countersunk holes for screws used for attachment to the prosthesis. The top assembly, primarily offering mediolateral and tilt adjustability, contains a 1-1/4 in., 1/8 in. increment scale for gauging mediolateral adjustments (with an index on the Fig. 1. An above-knee adjustable leg. single-flange toggle which is free to slide with respect to the top plate). A tilt scale2 is pro adjustment for adduction-abduction and vided by markings on the threaded bushings flexion-extension. of the four tilt-screw subassemblies. The

In Figure 5 are illustrated the major assem 2 blies of the coupling. The single-flange part of All scales have "neutral" positions highlighted. The "neutral" positions on the tilt scales are most important the toggle and the top plate constitute the in establishing the middle position of tilt, when top top assembly. The bottom assembly contains and bottom plates are parallel, or for disassembly, the "box" part of the toggle, the bottom plate, when it is important to "unlock" the coupling by the intermediate plate, the four tilt-screw having all four tilt screws down at least two incre subassemblies, and the toggle pin. The bottom ments below "neutral." 33

indexes for tilt scaling are the lower surfaces respect to the bottom plate. On the anterior of the knurled screws. Scale sensitivity for surface of the bottom plate is the 20-deg. tilt adjustment is 2 deg. (2-deg. increment) rotation scale. The index The bottom assembly provides rotation is located on the intermediate plate. The about the vertical axis and anteroposterior anteroposterior adjustment scale consists of adjustability because the intermediate plate a series of arcs, 1/8 in. apart for 1-3/4 in., etched (and toggle "box") is free to move with on the top surface of the bottom plate. The index for this scale is simply the outer contour of the intermediate plate. The coupling, made primarily from an aluminum alloy (except for the toggle assembly which is steel), weighs 12 oz., is 3-3/4 in. in diameter, and is 1-1/8 in. thick when the plates are parallel. Ranges of adjustment are as follows: 1. Mediolateral: Total Range—1-1/4 in. Increment of Scale Markings—1/8 in. 2. Anteroposterior: Total Range—1-3/4 in. Increment of Scale Markings—1/8 in. 3. Tilt: Total Range—10 deg. Increment of Scale Markings—2 deg. 4. Rotation: Total Range—20 deg. Increment of Scale Markings—2 deg. The coupling is disassembled by first lower ing each of the four tilt screws two increments on the tilt scale. This operation loosens the entire assembly because it is held together as a result of the forces produced by tightening the force screws, and the toggle pin can thus be disengaged from the toggle box and flange. The top assembly and bottom assembly can then be separated. Installation of the coupling into a prosthesis is made with the coupling so separated. Fig. 3. Alignment duplication jig. A, Adjustable leg mounted in jig. B, Adjustable leg has been removed and INSTALLATION OF THE COUPLING FOR DYNAMIC wooden set-up substituted. Prosthetist is sawing shank to proper length. ALIGNMENT {10) Figures 6 and 7 show the coupling in posi tion for dynamic-alignment trials. When installed, the coupling should be located as close as possible to the distal end of the stump. A piece of material may have to be added to accommodate the wood screws without affect ing the socket sealing plate itself. By so locat ing the coupling, small tilt adjustments on the coupling will produce major changes in the geometrical relationship of stump to prosthetic components distal to the coupling. When the "bench" or static alignment is reasonably close, the 10 deg. range of tilt adjustment is Fig. 4. The adjustable coupling assembled. more than adequate. 34

Fig. 5. Major assemblies and parts of the adjustable coupling. The toggle pin is permanently located in the semi circular channel just above the AA marks on the intermediate plate. From (10).

After the socket is constructed and the com with respect to the socket. The coupling is ponents approximately dimensioned3 length then set with all adjustments on "neutral" so wise, the top assembly of the coupling is that top plate and bottom plate are parallel attached to the bottom of the socket using and coaxial, care being taken to ensure that as many wood screws as possible (Fig. 8). the intermediate plate is not rotated with The bottom assembly then is attached to the respect to the bottom plate. top assembly by placing the single-flange part The socket with the coupling attached is of the toggle within the "box" part and pushing then temporarily placed on the above-knee the toggle pin through the holes in both toggle setup (knee-shank-foot) or on the below-knee parts. One must make certain that the "A" setup (shank-foot). A height check4 is made marks (or "P" marks) are located properly with the amputee standing on the prosthesis. 3 The over-all length of socket, knee unit, shank 4 With especially long above-knee stumps, the piece, and foot, plus 1-1/8 in. for the coupling, should knee center must be dropped during alignment trials be slightly larger than the amputee's dimensional because of the thickness of the coupling. Later, during requirements. Later sanding after a height check will transfer, true or near-true knee-center height can be produce accurate longitudinal dimensioning. restored. 35

Fig. 6. The coupling installed in an above-knee prosthesis.

Since the coupling has not been fully assem bled into the prosthesis, the prosthetist must, of course, assist the amputee in maintaining stability. After the height check has been made, the section of the prosthesis below the coupling (on the knee block or shank) can be sanded to obtain the correct height. One must consider the desired static or bench alignment before fully attaching the bottom plate assembly to the prosthesis. A Fig. 7. The coupling installed in a below-knee recently published chart (8) shows recom- prosthesis. From (10). 36

mended guides for "bench" alignment when the SACH foot is used. In any case, care should be exercised in locating the bottom assembly to assure that the ranges of adjustment avail able in the neutrally set coupling will not be exhausted during dynamic alignment. When the bottom plate is being installed, the countersunk clearance holes are made accessible by shifting the intermediate plate with respect to the bottom plate (Fig. 9). Dynamic alignment can begin when the coupling is reassembled and "locked" in the neutral position. This procedure should ordi narily be carried out in the following fixed sequence, making the linear adjustments first and the lilt adjustments second:

1. With the amputee seated, loosen only the two Fig 10. Use of the special compass for an alignment- front tilt screws and make the ANTEROPOSTERIOR ad transfer reference. The vertical reference lines will be justment. Tighten the two front screws. used to reestablish anteroposterior, mediolateral. and rotation positions. The horizontal line tangent to the tops of the compass arcs will reestablish tilt. From (10).

2. With the amputee seated, loosen only the two front till screws and make the MEDIOLATERAL adjust ment. Tighten the two front screws. 3. With the amputee standing, provide TILT adjust ment by turning down one of the two tilt screws on the side to be depressed (The screw should be turned down only as far as needed for the angular adjustment de sired.) Then tighten the till screw diagonally opposite to establish the angular adjustment desired. Next loosen (the same amount) the second screw on the side to be depressed and tighten the screw diagonalh" op posite to complete the angular adjustment and "lock" the coupling. 4. ROTATION may be established or reestablished before the screws are completely tightened in any of the Fig. 8. Attaching the top assembly of the coupling above three adjustments. The rotation scale reading to the bottom surface of the above-knee socket may be recorded before making any adjustment so that the position of rotation may be readily restored. Alignment Transfer No special jig is required for alignment transfer with the coupling. Actually, alignment is not "transferred" but rather "maintained" while the coupling is replaced with a per manent material. Around the periphery of the bottom plate of the coupling, there are ten radial holes located 36 deg. apart that serve as centers for a special compass which is used for scribing reference marks on the socket after dynamic alignment has been completed. The alignment Fig. 9. Attaching the bottom assembly of the coup compass is inserted in each of the holes in the ling to the top surface of the knee block. periphery of the bottom plate, and small arcs 37

are drawn or scribed on the socket base (Fig. 10). The tops of these arcs are then connected bv a circumferential line which will be exactly

Fig. 11. Using the band-saw to cut the socket im mediately below the horizontal-circumferential refer ence line.

Fig. 13. Replacement of the coupling with a 2-in. wood block. Coincidence of the vertical reference lines must be restored in the alignment- transfer process.

2 in. above the bottom surface of the bottom plate and parallel to it. At least four vertical reference lines (90 deg. apart) are made on the socket and con tinued onto the distal component (knee block or shank). The toggle pin of the coupling is removed and the top and bottom plate assemblies are Fig. 12. Sanding of the socket to the horizontal- detached from the socket and from the knee circumferential reference line, block (or shank). 38

A saw cut is then made in the socket base5 In addition, 34 above-knee and 22 below- just below the horizontal circumferential line knee sockets were replaced on existing pros (Fig. 11) and the socket base is sanded to the theses by use of the coupling. line (Fig. 12). A 2-inch-thick wood or foam Experience indicates some economic benefits block (with parallel top and bottom surfaces) in use of the adjustable coupling. Starting at is then placed between the socket and the the same point in an above-knee prosthesis knee block (or shank). The wood or foam block fabrication (with the socket roughly fitted), is then firmly attached (with cement, resin, the adjustable leg—transfer jig procedure and/or other fastening media) to both socket takes, on the average, slightly over 1/2 hr. more and knee block (or shank), care being taken than the coupling-compass procedure. The end to restore the coincidence of the vertical refer point for this time measure, in both proce ence lines on the assembled components (Fig. dures, is completion of alignment transfer 13). Although not necessary, an apparatus for with the prescribed prosthetic components holding the parts together during cement or assembled. resin cure can be used. A more significant advantage of the coupling If one wishes, the standard alignment trans accrues from its use in aligning above-knee fer jig may be used instead. Following stand prostheses when special knee or knee-ankle ard procedures, the prosthesis with the mechanisms have been prescribed. A pros coupling may be fixed in the jig and then the thesis system with functional features pro coupling removed. Saw cuts through the socket viding more than just a mechanical-friction base and knee block (or shank) and substitu control at the knee may require some deviation tion of an appropriately sized block of wood from that alignment which might be used will be needed. In the above-knee limb trans with only mechanical friction. Even an exten fer, one saw cut in the socket base will be sion bias strap will affect the alignment to be sufficient if the prosthesis is mounted in the used. Thus, for such devices as the Bock jig with the bottom plate of the coupling Safety Knee, the Hydra-Cadence (with a perfectly perpendicular to the long axis of relatively free plantar-flexion control), the the jig. Mauch hydraulic devices, polycentric linkages, and others, it is well to align the prosthesis EXPERIENCE WITH THE COUPLING with the prescribed special-function system installed. The coupling is designed primarily The coupling, although primarily designed for dynamic alignment of such systems. as a simple device for alignment of "perma Added to the economic advantage of one nent" lower-extremity prostheses, can also be device for both below-knee and above-knee used for temporary, or interim, prostheses. use is the simple and inexpensive process for The coupling has been in routine use in the alignment transfer. For a new shop, this Limb and Brace Section of the VA Prosthetics means that investment in an expensive jig is Center since March 1961. The numbers of not mandatory. Also, because of the compara permanent prostheses aligned with the coupling tively low cost of the coupling itself, many in the 22-month period ending December more alignment devices can be available in 31, 1962, were as follows: the shop. Thus, shifting alignment apparatus already installed in a setup awaiting an Hip-disarticulation .... 13 amputee trial may not need to be as frequent Above-knee 130 as formerly. Knee-bearing 16 "Bent"-knee. .... 3 The coupling also facilitates the alignment Below-knee 192 of replacement sockets. Fitting problems often require the fabrication of a completely new 5 Normally, if there is enough material here for the socket before the remaining parts of the pros wood screws to attach the coupling, there will be thesis need replacement. The new socket and enough material for this saw cut and the subsequent coupling can be installed on the "old" pros sanding without disturbing the socket itself. thesis for dynamic alignment and replacement- 39

Fig. 14. Special band-saw jig used by Danes during alignment transfer. This jig holds com ponents of the prosthesis in a fixed position to allow parallel band-saw cuts on both sides of the coupling. Subsequent clamping after cementing of wood block to replace coupling is also facili tated by this device.

socket fitting. This process is more expeditious slavia in 1961 (7). At about the same time, than one in which the adjustable leg is used Denmark became interested in its use. E. and then transfer is made to the "old" compo Lyquist of the Orthopaedic Hospital, Copen nents. Also, proper fairing of new socket to hagen, has published a report on the coupling6 "old" components can be assured by the and on the apparatus he designed for clamping coupling method of realignment because fairing the prosthesis on a band-saw bed for alignment problems can be readily observed and immedi transfer (J). See Figure 14. Dr. B. Zotovic of ately corrected. When the adjustable leg is Belgrade has kindly offered the photograph used, fairing problems can be noted only at (Fig. 15) of a prosthesis with the coupling now the time of transfer. Major corrective proce in use in Yugoslavia. In 1962, the coupling dures may then be necessary. was introduced into Argentina. Still more Many foreign practitioners have read and applications to foreign use are anticipated. appreciated the various United States' docu Many clinicians have realized the impor ments which have emphasized the importance tance of temporary or interim prostheses (P) of dynamic alignment. But also, many have for preliminary trials by an amputee. When felt frustrated for, even though they have temporary limbs which have alignment realized the value of dynamic-alignment adjustability are used, dynamic stump condi apparatus, economic or technical handicaps tioning and, especially for geriatric cases, prevented them from enjoying the use of the evaluation of an amputee's ability to cope devices the practitioners in the United States with a prosthesis are possible before a final had readily available. The coupling, therefore, prosthesis is ordered. Of utmost importance in because of its simplicity, can make a significant temporary limb use is that prosthesis "function contribution to the benefit of the disabled all 6 Lyquist (in November 1962) reported that the over the world, particularly in developing coupling was being used in all patellar-tendon-bearing areas. fittings at the Orthopaedic Hospital. Some above-knee The coupling was introduced into Yugo use was also reported. 40

Fig. 16. The adjustable couplingused with a plaster - of-Paris above-knee temporary sockel and an un finished knee shank. The three straps are eaeh 1/8 in by 3/4 in. low-carbon steel. From (9).

not be seriously compromised" (9). A well- fitted, soundly designed socket must be used, Fig. 15. A Yugoslav above-knee prosthesis incorporating the adjustable coupling tor dy and all parts should be continually maintained namic alignment. in proper alignment. Straps provide additional DYNAMIC ALIGNMENT VVTTH ADJUSTABLE COUPLING 41 reinforcement of socket to coupling assembly— mostly for horizontally directed loads. For plaster sockets, they are especially helpful since they can be contained within an outer, reinforcing plaster wrap. There are now available several devices which might be used for temporary prostheses (9). Among these is the coupling. Figure 16

Fig, 18. A temporary or interim prosthesis with the Northwestern adjustable below-knee pylon, plaster-of- Paris patellar-tendon-bearing socket and SACH foot, The three straps are similar to those of the previous two illustrations. An adaptor plate must be provided to iittach the straps to the pylon. In addition to the align ment adjustability available in the pylon, the position of the socket can still be altered if necessary.

illustrates a temporary or interim above-knee. Fig, 17. The adjustable coupling used with a prosthesis incorporating the coupling and plaster-of-Pa.ris below-knee temporary socket making possible the use of the type of knee and unfinished shank. The three straps have the (and function) anticipated for a permanent same cross-section as those used with the above- prosthesis. Now, not only fit and alignment knee socket. The position of the carbon steel can be '"tuned" to each other, but both can straps in both the above-knee and below-knee sockets should be reinforced with an extra be "tuned" to function. And, if necessary, plaster-of-Paris bandage wrap, as illustrated. function can possibly be altered by a rather 42

rapid change from one knee-shank mechanism to another. Figure 17 shows the coupling used in a below- knee temporary, or interim, prosthesis. For this level of amputation, the practitioner has the choice of the coupling or the Northwestern Adjustable Below-Knee Pylon shown in Figure 18. This apparatus also has sufficient align ment adjustability available for most below- knee applications in both temporary and permanent prostheses. When attached to a "permanent" (plastic or wood) socket, its advantage is that it can remain in the pros thesis after the dynamic-alignment process is complete.

FURTHER DEVELOPMENT The Northwestern Adjustable Below-Knee Pylon demonstrates a design principle long sought in alignment apparatus. With it, adjustments needed for dynamic alignment can be made as usual during the early stages of prosthesis fabrication, but the adjustable apparatus is now made a part of the limb obviating a transfer process but sometimes causing a slight increase in limb weight. At a later date, if the cosmetic-shank design allows it, readjustment of alignment can be made without a complete alteration of the prosthesis. Fig. 19. Schematic drawing of the "Wilson- Riblett wedge," as applied to the VAPC coup Use of a relatively flexible cosmetic cover will ling. probably be best for this purpose; if a plastic- covered foam shank is used, only destruction must be partly trimmed during the shaping of of the shank before realignment and a foam the limb for cosmetic finishing. Therefore, it replacement and plastic finishing after realign could probably not be used at a later date for ment will be required. realignment purposes. But still this device Most desirable would be one apparatus, will obviate transfer after initial alignment. perhaps coupling-like, which could be used in In eliminating only the primary-transfer above-knee and below-knee prostheses alike. process, a so-called "leave-in" alignment The present adjustable coupling is both too device must be priced at a level which would heavy and too expensive for this purpose. offer some gain to the prosthetist-user. If, at A. B. Wilson, Jr.7 and Victor T. Riblett8 have least with the regular coupling, alignment designed a simple and inexpensive plastic, transfer involves an investment of approxi tapered-disc device which might remain in mately $5.00 in labor and materials by the the prosthesis after the primary alignment limbshop, then the one-time, "leave-in" trials (Fig. 19). At present the device usually alignment device should cost somewhat less. But even so, possible saving per prosthesis or 7 Technical Director, CPRD, NAS-NRC, 2101 additional profit is of a very low order of Constitution Ave., Washington 25, D. C. magnitude. 8 Supervisor, Mechanical Development Branch, Army Prosthetics Research Laboratory, Walter Reed Needed is a device (and prosthesis design) Army Medical Center, Forest Glen Section, Washing which would allow realignment at a later date ton 12, D. C. without major reconstruction of the prosthesis. 43

Economic benefits would accrue to prosthetist even with present plastic-laminate finishing and amputee alike; at least some of the major methods, realignment would involve only cost-saving in the realignment process can be destruction of the laminate and then re- passed along to the customer. Perhaps many finishing. prostheses now condemned for alignment reasons would not need to be. LITERATURE CITED But most of all, such a device would offer 1. Anderson, Miles H., John J. Bray, and Charles A. convenience, allowing almost immediate ac Hennessy, Prosthetic principles, above-knee ampu tations (edited by Raymond E. Sollars), Charles commodation to an amputee's needs. Instead C Thomas, Springfield, Illinois, 1960. See espe of major delays in receiving a new alignment cially pp. 179-241. in a new or grossly altered older prosthesis, 2. Eberhart, Howard D., Herbert Elftman, and Verne rather prompt prosthetist attention can be T. Inman, The locomotor mechanism of the ampu tee, Chapter 16 in Klopsteg and Wilson's Human focused on an alignment problem in the existing limbs and their substitutes, McGraw-Hill, New limb. The prosthetist, if uncertain of an York, 1954. amputee's over-all fitting problem, can start 3. Lyquist, Erik, Jusieiingsapparat type VAPC oj with realignment of the existing prosthesis in overforingsapparat type OHK.14.01, Publikation his progressive analysis of the situation. He NR 1/62, Ortopaedisk Hospital, Kobenhavn. 4. Radcliffe, Charles W., Mechanical aids for align might be able to overcome what may seem to ment of lower-extremity prostheses, Artificial be socket-fit difficulties without major changes Limbs, May 1954, p. 20. there. But, in any case, he would have readily 5. Radcliffe, Charles W., Functional considerations in available the mechanism for study of the the fitting of above-knee prostheses, Artificial Limbs, problem and the problem's dependency on January 1955, p. 35. 6. Radcliffe, Charles W., Norman C. Johnson, and alignment. James Foort, Some experience with prosthetic Prosthesis design must of course be changed problems of above-knee amputees, Artificial Limbs, to accommodate the permanent installation of Spring 1957, p. 41. such a unit. A below-knee shank should 7. Staros, Anthony, and Henry Gardner, Report on orthotics-prosthetics research developments in Yugo preferably be a pylon—cosmetic-cover type, slavia, Department of Health, Education, and somewhat similar to the Northwestern device. Welfare, 1962. Preferably, the lower part of the above-knee 8. Veterans Administration Prosthetics Center, Sug limb thigh (where this device would be placed) gestions for fitting and aligning the SACH foot, should have an easily removable cosmetic a chart, May 1962. 9. Veterans Administration Prosthetics Center, cover. Perhaps a simple plastic finish over Temporary prostheses for lower-extremity ampu foam forced into the spaces around a light tees, Technical Report 1, September 1, 1962. weight, inexpensive coupling would be ade 10. Veterans Administration Prosthetics Center, Use quate. The foam would need to be cut away of the alignment coupling, a chart, July 1962. 11. Wagner, Edmond M., Contributions of the lower- (or possibly dissolved by appropriate chemical extremity prosthetics program, Artificial Limbs, means) when realignment was necessary. But May 1954, p. 8.